System and method for determining the level of a substance in a container based on measurement of resonance from an acoustic circuit that includes unfilled space within the container that changes size as substance is added or removed from the container

ABSTRACT

Level of substance in a container can be determined by exciting vapor in unfilled space within the container. Variable frequency oscillator and emitting transducer can provide signals to excite resonance of vapor. Sensors can measure the peak resonant signal of vapor excited in unfilled space within the container as the amount of substance in the container changes. A signal-processing unit coupled to the sensor and variable frequency oscillator can process signals sensed by the sensing transducer and can extract them from background noise affecting the acoustic signal of the system using correlation functions by referencing the signal generated by the variable frequency oscillator. A computer can obtain the sign processed by the signal-processing unit and calculate the unfilled space within the container and derive therefrom an amount of filled space representing the amount of the substance contained therein. A gauge can indicate the amount of substance in the container.

STATEMENT OF PRIORITY

The present application is a continuation-in-part of nonprovisionalpatent application Ser. No. 14/596,375, entitled “System and Method forDetermining the Level of a Substance in a Container Based on Measurementof Resonance from an Acoustic Circuit that Includes Unfilled Spacewithin the Container that Changes Size as Substance is Added or Removedfrom the Container,” filed Jan. 14, 2015. Patent application Ser. No.14/596,375 is incorporated herein by reference in its entirety.

Patent application Ser. No. 14/596,375 is a continuation-in-part ofnonprovisional patent application Ser. No. 13/673,555, entitled “Systemand Method for Determining the Level of a Substance in a Container Basedon Measurement of Resonance from an Acoustic Circuit that IncludesUnfilled Space within the Container that Changes Size as Substance isAdded or Removed from the Container,” filed Nov. 9, 2012, which isherein incorporated by reference in its entirety.

The present application claims the priority and benefit of patentapplication Ser. No. 14/596,375 and patent application Ser. No.13/673,555.

TECHNICAL FIELD

The present invention is generally related to measurement devices usedto measure the level of a substance (e.g., liquid or solid) within acontainer (e.g., a vessel, tank, room). The present invention is moreparticularly related to systems and methods for determining the amountof liquid within a container by measuring the resonance from an acousticcircuit including an empty space as a component of the acoustic circuitwithin the container that changes in size as the amount of the substanceis added or removed from the container.

BACKGROUND

A fuel gauge is an instrument used to indicate the level of fuelcontained in a tank. Although commonly used in automobiles, similargauges can also be used to determine the substance level for any tankincluding underground fuel storage tanks.

When used in automobiles, the fuel gauge typically consists of twoparts: the sensing unit and the indicator. The sensing unit usually usesa float connected to a potentiometer. The indicator is usually mountedin a dashboard of modern automobiles and typically includes a needlecalibrated to point to a scale consisting of printed ink designed as ametered analog gauge with a needle indicating the level of fuel thatremains in a tank based on where the needle is pointing to on the gauge.As the tank empties, the float drops and slides a moving contact along aresistor, increasing its resistance. In addition, when the resistance isat a certain point, it will also typically turn on a “low fuel” light onsome vehicles.

There are many problems with the current state of the art for liquidlevel measurement. The principle problem is that the float system is notlinear. When the float is horizontal it accurately measures the level offluid in the tank. As the float becomes more vertical, it is no longeraccurate. Also, irregularities in the shape and position of the tank mayaffect the accuracy of the system. Therefore, there is a need foranother safer, non-contact based method for fuel level to be determined.Modern vehicles usually have a computer that calculates “miles toempty”, but the older system of electrical measurement causes wildfluctuations in the calculations; therefore, a vehicle operator cannotcompletely rely on the accuracy of the system when planning a futurestop to refuel.

Helmholtz resonance is the phenomenon of air resonance within a cavitysuch as the noise that occurs when one blows across the top of an emptybottle. The air in the port or tube (also referred to as the neck of thechamber) has mass and friction with the walls of the tube. A longer tubewould make for a larger mass and more friction and vice-versa. Thediameter of the tube is also related to the mass of air. The resonanceof a bottle can change as liquid is added inside the bottle. The presentinventor believes that Helmholtz resonance can be used to measuresubstance by measuring the unfilled space (unfilled with respect to asubstance, but containing a vapor) in a container allowing thecalculation of the amount of substance filling the container, which isthe primary goal of the present invention, for which details will now befurther described below. Resonant signals vary in frequency andamplitude.

BRIEF SUMMARY

It is a feature of the present invention to provide a system fordetermining the amount of substance within a container by measuring theresonance from an acoustic circuit including unfilled space as acomponent of the acoustic circuit within the container that changes insize as the amount of the substance is added or removed from thecontainer.

It is another feature of the present invention to include in the systeman emitting transducer providing a signal generated by a variablefrequency oscillator to excite acoustic resonance of an acoustic circuitrepresented by a container having an unfilled space containing vaporanalogous to a capacitor of an acoustic circuit, and a tube (which canbe variable in length for tuning) analogous to an inductor of anacoustic circuit, and the vapor experiences friction as it moves withinthe tube, which is analogous to a resistor of an acoustic circuit. Thetube may have an opening that can be capped by a metal disc including aflexible seal connecting the outer perimeter of the cap with the mouthof an opening associated with the tube.

It is yet another feature of the present invention to provide a sensingtransducer for measuring the amplitude of the signal as it changes asthe circuit achieves resonance and as the container is filled orempties.

It is another feature of the present invention to provide asignal-processing unit that can be coupled to the sensing transducer andto the variable frequency oscillator that is driving the emittingtransducer. The signal-processing unit can process the signal sensed bythe sensing transducer to extract it from any background noise affectingthe acoustic resonance system using correlation functions by referencingthe signal generated by the variable frequency oscillator.

It is another feature of the present invention to provide a computerwherein the signal processed by the signal-processing unit is providedto the computer to calculate the empty space of the container and thusderive an amount of filled space representing the amount of thesubstance in the container.

It is another feature of the present invention to provide a gauge incommunication with the computer to provide a readout or indication ofhow much substance is in the container and/or an estimate of when thesubstance will be depleted.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a block diagram of a system for measuring the levelof a substance in a container.

FIG. 2 illustrates a block diagram of a system for measuring the levelof substance in a container including a tube that can be varied inlength to enable turning of the acoustic circuit. Also shown is a capthat can be used to seal an opening formed at an end of said tube andcan be attached to the opening with a flexible surround around the cap'sperimeter, because the lid should be able to freely move as the systemresonates.

FIGS. 3A through 3C illustrate charts of resonant signals measured whena container is near empty, half empty, and near full.

FIG. 4 illustrates a flow diagram of a method for determining the levelof a substance in a container.

FIG. 5 illustrates the system described in FIG. 1 where correlationsoftware can be used by a signal-processing unit and/or computer toprocess signals sensed by the sensing transducer and extract them fromany background noise affecting the acoustic resonance system usingcorrelation functions by referencing the signal generated by thevariable frequency oscillator.

FIG. 6 illustrates the system described in FIG. 5 including a device formeasuring the speed of sound inside the container.

FIGS. 7A-7C illustrate alternative configurations of devices formeasuring the speed of sound inside the container.

FIGS. 8A-8D illustrate alternative configurations for caps, associatedwith systems and methods for measuring the level of substance in acontainer.

FIGS. 9A-9D illustrate the principle of cross-correlation as it relatesto systems and methods for measuring the level of substance in acontainer.

FIG. 10 illustrates the amplitude of a resonator as a function offrequency as it relates to systems and method for measuring the level ofsubstance in a container.

FIG. 11 illustrates a block diagram of an alternative embodiment of asystem for measuring the level of a substance in a container.

FIGS. 12A-12C illustrate alternative configurations of bafflesassociated with an alternative embodiment of a system for measuring thelevel of a substance in a container.

FIG. 13 illustrates a block diagram of another alternative embodiment ofa system for measuring the level of a substance in a container.

FIG. 14 illustrates a block diagram of another alternative embodiment ofa system for measuring the level of a substance in a container.

DETAILED DESCRIPTION

Referring to FIG. 1, a system 100 is illustrated for measuring the levelof a substance in a container. The system 100 includes an emittingtransducer 110 that can provide a signal generated by a variablefrequency oscillator 115 in an unfilled space 106 containing a vapor 125(substance empty, vapor-filled space) located within a container 105that is also containing a substance 130 within filled space 107. Signalsfrom the emitting transducer 110 excite acoustic resonance of anacoustic circuit represented by a container 105, the unfilled space 106filled with vapor 125 (analogous to a capacitor of an acoustic circuit).A tube 140 analogous to an inductor of an acoustic circuit can beprovided wherein the vapor 125 (also found in the tube) experiencesfriction as it moves within the tube 140. The vapor 125 is analogous toa resistor of an acoustic circuit.

A sensing transducer 150 mounted on the container 105 measures resonance(amplitude and frequency of signal) as it changes when the resonantcircuit achieves resonance in the tube 140 as substance 130 is added orremoved from the container 105. A signal-processing unit 160 can becoupled to the sensing transducer 150 and to the variable frequencyoscillator 115 that is driving signals to the emitting transducer 110.The signal-processing unit 160 processes resonant signals sensed by thesensing transducer 150 with reference to signals generated by thevariable frequency generator 115 and can extract the resonant signalsfrom background noise using correlation functions.

A computer 170 can be provided in the system wherein signals processedby the signal-processing unit 160 are provided to the computer 170 tocalculate the unfilled space 106 of the container 105 and thus derive anamount of substance 130 contained by filled space representing theamount of the substance 130 in the container 105. A gauge 180 (e.g.,digital readout, analog readout, etc.) can be provided in communicationwith the computer 170 to provide a readout or indication of at least oneof: how much substance is in the container, an estimate of when thesubstance will be depleted, and the rate of substance depletion (e.g.,when substance is being used as a combustible in a power generatingsystem).

Referring to FIG. 2, the tube 140 can be varied in length to enabletuning and/or calibration of the acoustic circuit. A cap 145 can be usedto seal an opening 143 formed at an end of said tube 140. The cap 145can be attached to the opening with a flexible surround 147 around thecaps perimeter, because the lid should be able to freely move as thesystem resonates.

Alternative embodiments of cap 145 are shown in FIGS. BA-C. FIG. 8Aillustrates a cap 145 in accordance with a preferred embodiment of theinvention. In this embodiment, cap 145 is shown connected to tube 140.Cap 145 is configured of a ridged base ring 805 and a ridged top ring810. The joint between the base ring 805 and top ring 810 holds aflexible upper 820. The center of the flexible upper is configured witha high-density top cap or weight 815. The high-density top cap 815 isconfigured of a material that is dense and therefore relatively heavyfor its size. High-density top cap 815 is optional. Helmholtz resonanceis best achieved when tube 140 is left open. However, for manyapplications, such as vehicle gas tanks, it is impractical or illegal toleave tube 140 uncovered. The flexible cap 145 is configured to allowflexible upper 820 to move so that the Helmholtz resonance inside thetank is affected as little as possible. In a preferred embodiment,flexible upper 820 is formed with concentric folds that allow theflexible upper 820 and high-density top cap 815 to rest in a relativelyflat plane above the tank (as shown in FIG. 12B). When the flexibleupper is perturb, for example, by pressure waves in tank 105, the extramaterial in the folds allows the flexible upper to extend upward ordownward.

FIG. 8B illustrates an alternative embodiment of cap 145 wherein thehigh density top cap 815 is fitted with an additional weight 825. FIG.8C illustrates a top view of top ring 810 and in particular the inneredge 830 of top ring 810 which can be configured to be threaded alongwith base ring 805 as shown by threads 835 in FIG. 8D. Cap 145 can beinstalled on tube 140 via a threaded connection as shown.

The sensing transducer 150 can be mounted in the tube 140 extending fromthe container 105, although it can be possible to mount the sensingtransducer 150 at other areas around the container 105. In some tanks,it may be necessary to include a separate fill tube 103 for use ininserting or removing substance from the tank. A separate fill tube 103will prevent the sensing transducer 150 and tube 140 from becomingdisturbed or damaged. It should be appreciated that other tubing may beused in connection with the system but do not require disclosure hereinto understand the present invention. Examples of additional tubinginclude fuel lines as used to deliver fuel to the combustion system orengine in an automobile.

Referring to FIGS. 3A-3C, charts of resonant signals measured when acontainer is near empty, half empty, and near full are shown. A qualityfactor or “Q,” for the resonant frequency is an important considerationin accurately measuring the level of substance in a tank. Resonatorswith a high “Q” resonate with greater amplitudes at the resonantfrequency and have a smaller range of frequencies around that frequency.Thus, the disclosed high-Q acoustical circuit does a better job offiltering out unwanted signals nearby on the spectrum than a similarresonator with a low “Q”. Further, high “Q” resonators oscillate in asmaller range of frequencies and are generally more stable. In thepresently disclosed acoustical circuit, the quality factor needs to bevery high to ensure accuracy. As the quality factor decreases, theaccuracy of the level measurement also decreases. Mathematically thequality factor “Q” can be expressed as shown in equation (1).Q=fc/Δf  (1)where fc is the resonant frequency and Δf is the half-power bandwidth.FIG. 10 illustrates two signals, one with a high Q and one with a low Q.In FIG. 10, amplitude is shown as a function of frequency. Signal 1005illustrates a resonant frequency curve with a low quality factor. Thiscan be seen by the relatively large half-power bandwidth of the signal1025 at the resonant frequency 1005. By contrast, the peak 1030 ofsignal 1010 has a much higher amplitude at resonant frequency 1005 andhas a much more narrow half-power bandwidth between frequencies 1015 and1020. In a preferred embodiment, the acoustical circuit disclosed hereinis configured to have a very high “Q” which is preferably less than athree cycle shift.

Referring to the flow diagram 400 in FIG. 4, a method for determiningthe level of a substance in a container is described. As shown in block410, vapor in an unfilled space 106 within a container 105 holding asubstance 130 is excited by a resonant signal provided from an emittingtransducer 110 coupled to a variable frequency oscillator 115 providingsignals to the emitting transducer 110 that excite resonance. Then asensor 150 is used to measure the resonant signal of the vapor 125excited by the signal from the emitting transducer 110 as shown in block420. The resonant signal is a component of an acoustic circuit createdby the unfilled space 106 that changes as the amount of the substance130 is added or removed from the container 105. The sensor 150 candetect the frequency and amplitude of resonant signals created in thetube 140 and unfilled space 106 associated with the container andextending away from the unfilled space 106. The resonant circuit createdby vapor 125 in the container's unfilled space and the tube achievesresonance as substance 130 within container 105 is added or removed fromthe container 105.

In an alternative embodiment, block 410 can include periodical impulseexcitation. In a bounded domain such as tank 105, a single wave (forexample, the wave produced by emitter 110) becomes a series of resonantfrequencies as they are reflected between the walls of the tank. As aresult, the bounded wave resonates at multiple frequencies. This makesdetection of the resonant frequency more difficult. In order to overcomethis problem, emitter 110 can periodically emit a signal to “kick” theresonant frequencies. These frequencies will then diminish to zero atvarying rates with the fundamental frequency which is a property of theresonating body and the frequency of interest, remaining longest. As aresult, this frequency can be identified by kicking the frequencies inthe resonator with emitter 110 and then identifying the remainingfrequency which is indicative of the resonant frequency of interest andcan be used to measure the level of a substance in the tank.

Referring to FIG. 5, the system 100 described in FIG. 1 is shown wherecorrelation software 505 can be used by a signal-processing unit 160and/or computer 170 to process signals sensed by the sensing transducer150 and extracts them from any background noise affecting the acousticresonance system using correlation functions by referencing the signalgenerated by the variable frequency oscillator 115. A signal-processingunit 160 can be provided and coupled to the sensing transducer 150 andto the variable frequency oscillator 115 that is driving the emittingtransducer 110 in order to process signals using correlation.

Container 105 is very likely to be disposed in a noisy environment. Forexample, container 105 may be a gas tank on a car. In a typical carride, the gas tank of the vehicle is exposed to traffic noise, enginevibration, etc. Additionally, the fact that the Helmholtz resonator(i.e., container 105) must be capped means that the loudness of the toneis dampened making it very hard to detect. The methods and systemsdisclosed herein require identification of very specific frequencies inorder to accurately measure the unfilled space 106. However, thefrequencies themselves are intrinsically noisy, and therefore difficultto detect. These endemic problems must be solved in order to accuratelymeasure the unfilled space 106 in the container.

In one embodiment, software 505 can be used by the signal-processingunit 160 and computer 170 to implement a cross-correlation (orauto-correlation) technique to aid in the identification of relevantfrequencies. Cross-correlation can be understood as a measure of thesimilarity of two waveforms as a function of time lag applied to one ofthem.

FIGS. 9A-D illustrate how cross-correlation can be used to lift theresonant frequency out of the background noise inevitably present intank 105. In FIG. 9A, signal strength is illustrated as a function oftime. In, for example, a tank 105, the signal strength of noise 910 willbe significant compared to the resonant signal 905 as shown. This makesit very difficult to identify the resonant frequency, and by extension,determine the level of the substance 130 in tank 105. However, as shownin FIG. 9B, the application of a cross-correlation technique makesidentification of the resonant frequency more reliable. As the signal isshifted and delayed by one cycle, the amplitude of the desired signal905 increase by more than the noise 910. In FIG. 9C, the signal has beenshifted and delayed by two cycles. Again, the amplitude of the desiredsignal 905 increase much more than that of noise 910. FIG. 9Dillustrates the application of a cross-correlation technique where thesignal is shifted and delayed by many cycles. As illustrated, after manycycles the amplitude of signal 905 has a dramatically higher amplitudethan noise 910. Thus, FIG. 9D shows how the desired signal 905 has beenlifted out of noise 910 and is therefore much easier to measure.

As applied in the present embodiment, the frequency associated with theresonant signal provided from the emitting transducer 110 coupled to avariable frequency oscillator 115 can be provided to software 505. Theresonant signal collected from sensor 150 can also be provided tosoftware 505. Software 505 is configured to delay one of the emittedsignal or the recorded signal in time. The signal is delayed in manysteps in order to simulate the discrete time steps as a continuousvariable (i.e., time). For example, the time delayed steps may rangefrom 1 Hz to many thousands of Hz or more as required. As the “sliding”signal (that signal being time delayed) is shifted, the emitted andrecorded signals are integrated (or summed). When the two respectivesignals align the integration is additive, highlighting the similarityand “lifting” it from the noise. The noise associated with each signalis also additive, but because it is random sums much more slowly. Thisis a result of the fact that when the sum of the signals is a sum ofpressures whereas the sum of noise is a sum of powers. Each time thenumber of delayed cycles is doubled, the signal to noise ratio improvesby approximately 3 dB. Cross-correlation is preferred over other signalprocessing methods such as Fast Fourier Transforms (FFTs) because FFTsare not target to the desired frequency. Cross-correlation can be usedto lift the specific, in this case resonant, frequency alone out of thenoise, which is critical for accurate level measurement.

Software 505 is thus configured to identify the summation of the twosignals above some threshold as indicative of the frequency associatedwith the resonance in the container 105. This can then be used todetermine the amount of unfilled space 106 in the container 105, and inturn the amount of substance 130 in the container 105.

A computer 170 is provided to obtain the signal processed by thesignal-processing unit 160 and calculate unfilled space 106 within thecontainer 105 and derive therefrom an amount of filled space 107representing the amount of the substance 130 contained within thecontainer 105.

A gauge 180 can, be provided in communication with the computer 170 toprovide a readout or analog indication of at least one of how muchsubstance is in the container 105, an estimate of when the substancewill be depleted, and the efficiency of substance depletion. Theefficiency of substance depletion is a measure of vehicle efficiency,such as the vehicle's miles traveled per gallon of fuel or “mileage”).It can be determined by determining the amount of fuel the vehicle hasused to travel a given distance (for example, in a car).

In many applications, the unfilled space 106 in container 105 isoccupied by a vapor 125 resulting from the substance 130 held in thecontainer 105. In gases temperature, molecular composition, pressure,and heat capacity ratio can all change the speed that sound travelsthrough the gas. For purposes of this invention it is important tounderstand that the frequency of a resonator is dependent on thetemperature and volume of the resonator. Together, these dictate thefrequency produced by the oscillator. The speed of sound can be simplydetermined by the wavelength of the sound multiplied by the frequency ofthe sound. If the speed of sound changes, so too will the frequency.Thus, the speed of sound must be determined in order to accuratelydetermine the unfilled space in the container.

In one embodiment, a tube 605 can be provided in the container 105. Thetube 605 can include a conduit 610 to rigidly support the tube 605 inthe unfilled space 106 in the container 105. The conduit 610 can alsoprovide an electrical connection between a piezoelectric transducer 615on one end of the tube 605 and a signal generator (e.g., a computer 170)associated with the system. The second end of the tube 605 is left openso that the vapor 125 present in the unfilled space 106 in the container105 also occupies the unfilled space inside the tube 605.

The piezoelectric transducer 615 can be signaled by the signalgenerating computer 170 to send a “ping” of known frequency down thetube 605. The frequency of the “ping” should be selected to notinterfere with the resonance of the Helmholtz resonator. The signal“ping” is reflected back from the open end of the tube 605 and detectedby the transducer 615 which provides a signal to computer 170. Thelength of the tube 605 is known and the signal generating computer 170can measure the time lapse between the signal ping generation and thedetection of the reflected response. From this information, the speed ofthe sound traveling through the vapor 125 can be calculated.

The speed of sound in the container 105 can and should be measuredregularly, for example, every few seconds, once a minute, or once anhour. Regular recalculation is necessary because, as the amount ofsubstance 130 occupying the container 105 changes, the content of thevapor 125 can also change, the temperature within the container 105 maychange, etc., and concurrently the speed of sound in the container 105may change.

FIGS. 7A-C, a series of alternative configurations for speed of sounddetectors are illustrated. FIG. 7A illustrates the tube arrangement 600shown deployed in FIG. 6. Equivalent or identical features of thesearrangements are labeled with equivalent reference numerals.

In FIG. 7B, a U-shaped bracket 705 can be fitted inside the container105. The U-shaped bracket 705 can be mounted to the inside of thecontainer 105 or alternatively can be mounted to a conduit 610. On oneend, the U-shaped bracket 705 can be fitted with a piezoelectrictransducer 615. The signal generating computer 170 can signal thetransducer 615 to generate a signal ping. A second transducer 616 can beconfigured on the opposite wall of the U-shaped bracket 705 and cansignal the computer 170 upon detection of the signal ping. It isimportant that U-shaped bracket 705 be mounted inside container 105 withthe open side of the U-shape pointed toward the substance 130 to allowthe free flow of vapor 125 inside and between the walls of the U-shapedbracket 705 so that the signal ping travels through the vapor 125.

FIG. 7C illustrates that the U-shaped bracket 705 is fitted with asingle Piezoelectric transducer 615 on one wall of the bracket 705. Onthe opposite wall of the bracket 705, a reflecting plate 710 can beprovided. The signal-generating computer 170 can signal thepiezoelectric transducer 615 to generate a signal ping. The signal pingis reflected off of the reflecting plate 710 and back to thepiezoelectric transducer 615 which signals be computer 170 to record thesignal ping detection.

In each of the three embodiments shown in FIGS. 7A-7C, the speed ofsound can be calculated using the known distance the signal ping travelsfrom its generation at Piezoelectric transducer 615 to detection andusing the time it takes for the signal ping to travel that distance. Ineach of the embodiments, the function of the mounting apparatus (e.g.,tube 605 or U-shaped bracket 705) is important because they allow thevapor to naturally occupy the space through which the signal pingtravels.

FIG. 11 illustrates an alternative embodiment of a system 1100 whereinthe level of the substance in tank 105 can be identified by passivelyexciting a resonant signal in the tank 105. In this embodiment, adeflector baffle 1110 is fixed over the flexible cap 145, in a deflectorbaffle assembly 1105. When a vehicle associated with tank 105 is inmotion, ambient air will effectively flow over tank 105. The deflectorbaffle 1110 is designed to direct this air over the flexible cap 145 ontube 140. When the deflected air moves over the flexible cap 145, thecap 145 can vibrate exciting acoustic resonance of an acoustic circuitrepresented by the container 105 having an unfilled space containingvapor analogous to a capacitor of an acoustic circuit, and the tube 140(which can be variable in length for tuning) analogous to the inductorof an acoustic circuit. The vapor in the tank 105 experiences frictionas it moves within the tube 140, which is analogous to a resistor of anacoustic circuit.

As described above for other embodiments, in this embodiment a sensingtransducer 150 mounted on the container 105 measures resonance(amplitude and frequency of signal) passively driven by the air flowingover cap 145, as it changes when the resonant circuit achieves resonancein the tube 140 as substance 130 is added or removed from the container105. A signal-processing unit 160 can be coupled to the sensingtransducer 150. The signal-processing unit 160 processes resonantsignals sensed by the sensing transducer 150 with reference to signalsgenerated by the passively driven vibration of the flexible cap 145 andcan extract the resonant signals from background noise usingauto-correlation functions.

A computer 170 can be provided in the system wherein signals processedby the signal-processing unit 160 are provided to the computer 170 tocalculate the unfilled space 106 of the container 105 and thus passivelyderive an amount of substance 130 contained by filled space representingthe amount of the substance 130 in the container 105. A gauge 180 (e.g.,digital readout, analog readout, etc.) can be provided in communicationwith the computer 170 to provide a readout or indication of at least oneof: how much substance is in the container, an estimate of when thesubstance will be depleted, and the rate of substance depletion.

FIG. 12A illustrates the deflector baffle and flexible cap assembly1105. The deflector baffle 1110 can be comprised of a curved wind catch1110 a. The wind catch 1110 a is formed over the flexible cap 145 sothat as the tank 105 is moved through the air, the air (which is movingrelative to the tank) is caught by the wind catch 1110 a and directedover the flexible cap 145. The wind catch 1110 a is held over theflexible cap 145 with struts 1120. FIG. 12A illustrates two struts 1120,but more or fewer may also be used depending on design considerations.

FIG. 12B illustrates flexible cap 145. It is important to notice thatflexible cap 145 shown in FIG. 12B includes upper 820, which isconfigured to be folded 820 a at the edges and includes a weightedmember 815. This design allows the flexible cap 145 to vibrate when windis pushed over it, thereby exciting a resonant signal in the tank 105.

FIG. 12C illustrates an alternative embodiment wherein the deflectorbaffle 1110 assembly is deployed over an opening 1205 in tank 105,rather than over a cap 145. In this embodiment, the opening of tube 140is left uncapped. When air is directed over the opening 1205 bydeflector baffle 1110, the wind creates pressure waves in the tube 140which excite a resonant signal in the tank 105.

FIG. 13 illustrates yet another alternative embodiment of the system1300 wherein the deflector baffle is designed to be a flat air scoop1305. In this embodiment, the air scoop 1305 is tapered with a largerend 1315 facing the incoming air 1310 and the tapered end 1320 formedabout the flexible cap 145. As arrows 1310 indicate, ambient air flowingover tank 105 is directed over the tube 140 with flexible cap 145 by airscoop 1305. The it scoop 1305 can be fixedly connected to tank 105 viaweld rivets, jointing compound, screws, cement, nails, or other suchconnection means. It should be appreciated that in this embodiment tubecan be arranged with or without flexible cap 145 depending on designconsiderations. It should also be understood that the shape of air scoop1305 may vary depending on design considerations.

FIG. 14 illustrates another embodiment of system 100 for measuring thelevel of a substance in a container. The system 100 includes an emittingtransducer 110 that can provide a signal generated by a variablefrequency oscillator 115 in an unfilled space 106 containing a vapor 125(substance empty, vapor-filled space) located within a container 105that is also containing a substance 130 within filled space 107. Signalsfrom the emitting transducer 110 excite acoustic resonance of anacoustic circuit represented by a container 105, the unfilled space 106filled with vapor 125 (analogous to a capacitor of an acoustic circuit).A tube 140 analogous to an inductor of an acoustic circuit can beprovided wherein the vapor 125 (also found in the tube) experiencesfriction as it moves within the tube 140. The vapor 125 is analogous toa resistor of an acoustic circuit.

A sensing transducer 150 mounted on the container 105 measures resonance(amplitude and frequency of signal) as it changes when the resonantcircuit achieves resonance in the tube 140 as substance 130 is added orremoved from the container 105. A signal-processing unit 160 can becoupled to the sensing transducer 150 and to the variable frequencyoscillator 115 that is driving signals to the emitting transducer 110.The signal-processing unit 160 processes resonant signals sensed by thesensing transducer 150 with reference to signals generated by thevariable frequency generator 115 and can extract the resonant signalsfrom background noise using correlation functions.

A computer 170 can be provided in the system wherein signals processedby the signal-processing unit 160 are provided to the computer 170 tocalculate the unfilled space 106 of the container 105 and thus derive anamount of substance 130 contained by filled space representing theamount of the substance 130 in the container 105. A gauge 180 (e.g.,digital readout, analog readout, etc.) can be provided in communicationwith the computer 170 to provide a readout or indication of at least oneof: how much substance is in the container, an estimate of when thesubstance will be depleted, and the rate of substance depletion (e.g.,when substance is being used as a combustible in a power generatingsystem).

The system further includes a temperature sensor 1400 configured formeasuring the temperature of the liquid inside the container. As thetemperature of liquid 130 changes, for example, due to changingtemperatures in the surrounding external environment, the liquid'svolume also changes. This can affect the accuracy of the determinationof the unfilled space 106 in container 105. The temperature sensor 1400is connected to computer 170 and can be used to compute a change in thevolume of the liquid 130 resulting from temperature change of theliquid. The change in the volume of the liquid can be used to adjust thecalculation of the unfilled space 106 of the container 105 and thusderive an amount of substance 130 contained by filled space representingthe amount of the substance 130 in the container 105.

The temperature sensor 1400 may comprise a thermometer that is resistantto the corrosive effects of the liquid 130. The thermometer 1400 isillustrated as attached to the lower portion of the interior of tank105. The temperature sensor must be attached to the tank such that it isin operable connection with the liquid 130. As such, the temperaturesensor 1400 can be attached to the interior of the tank at or near thebottom of the tank 105. It should further be appreciated that thetemperature sensor may be used with any combination of the embodimentsdisclosed herein.

The invention claimed is:
 1. A system for measuring the volume of asubstance in a container, comprising: an emitting transducer providing asignal generated by a variable frequency oscillator to excite acousticresonance of an acoustic circuit represented by a container having anunfilled space filled with a vapor analogous to a capacitor of anacoustic circuit, and a tube analogous to an inductor of an acousticcircuit, wherein the vapor experiences friction as it moves within thetube, which is analogous to a resistor of an acoustic circuit; a sensingtransducer measuring amplitude of the signal as it changes as thecircuit achieves resonance and as the container is filled or emptied; aspeed of sound transducer configured to emit and detect a signal pinginside said container to determine a speed of sound in said container; atemperature sensor for measuring a temperature of said substance; and asignal processing unit coupled to the sensing transducer and thevariable frequency oscillator driving the emitting transducer, saidsignal processing unit processing the signal sensed by the sensingtransducer to extract it from background noise by referencing the signalgenerated by the variable frequency oscillator and shifting said sensedsignal by one or more cycles according to a cross-correlation technique,and wherein a frequency decrease in the sensed signal is indicative of adecrease in the volume of the substance in the container.
 2. The systemof claim 1, further comprising a computer associated with said signalprocessor wherein said correlation functions comprise cross-correlationfunctions.
 3. The system of claim 2, wherein the signal processed by thesignal processing unit is provided to the computer to calculate theunfilled space of the container and thus derive an amount of filledspace representing the amount of the substance in the container.
 4. Thesystem of claim 3, further comprising a gauge in communication with thecomputer to provide a readout or indication of at least one of: how muchsubstance is in the container, an estimate of when the substance will bedepleted, and the rate of substance depletion when substance is beingused as a combustible in a power generating system.
 5. The system ofclaim 4, wherein said tube is variable in length to enable tuning of theacoustic circuit.
 6. The system of claim 5, further comprising a capcapping an opening formed at an end of said tube, wherein said capcomprises a ridged ring, a flexible upper, and a high density top cap.7. The system of claim 1 further comprising: a conduit connecting saidcontainer to a tube wherein said speed of sound transducer is configuredon one end of said tube.
 8. The system of claim 1 further comprising: aconduit connecting said container to a U-shaped bracket wherein saidspeed of sound transducer is configured on one side of said U-shapedbracket and a reflecting plate is configured on an opposite side of saidU-shaped bracket.
 9. The system of claim 1 wherein said signal has ahigh quality factor.
 10. The system of claim 1 further comprising: aconduit connecting said container to a U-shaped bracket wherein saidspeed of sound transducer is configured on one side of said U-shapedbracket and a second speed of sound transducer is configured on anopposite side of said U-shaped bracket.